Measurements and modeling of transmitted power of EC waves propagating for normal and oblique injection in FTU tokamak during ECRH experiments at 140 GHz

A continuous monitor of waves absorption during ECRH experiments is performed by a set of three low-gain probes, installed in the FTU tokamak walls, collecting the residual scattered and depolarized RF radiation. One probe is located in the same sector of the launching system; the other two are toroidally displaced by 60deg and 90deg respectively. Two gyrotrons at 140 GHz delivering 0.5 MW each up to 0.5 s have been used to inject EC waves from the low field side at the fundamental harmonic ordinary mode. The estimated of the transmitted power is carried out by a 3D ray-tracing code taking into account both the beam diffraction effects and a statistical model for describing multiple reflections and scrambling of polarization at the tokamak walls. Fair agreement is found between the measured and calculated values of residual electromagnetic radiation. (author)